model: add PkgItem.prettify_xml()

Author: Steve Canny

opcdiag/model.py

@@ -188,7 +188,11 @@ def prettify_xml(self):
         Reformat the XML in this package item to indented, human-readable
         form. Does nothing if this package item does not contain XML.
         """
-        raise NotImplementedError
+        if self.is_content_types or self.is_xml_part or self.is_rels_item:
+            self._blob = etree.tostring(
+                self.element, encoding='UTF-8', standalone=True,
+                pretty_print=True
+            )
 
     @property
     def uri(self):

tests/test_model.py

@@ -236,3 +236,14 @@ def it_can_calculate_its_effective_path(self):
         expected_path = ('root_uri\\uri' if sys.platform.startswith('win')
                          else 'root_uri/uri')
         assert pkg_item.path == expected_path
+
+    def it_can_prettify_its_xml(self):
+        blob = '<foo><bar/></foo>'
+        pkg_item = PkgItem(None, 'foo.xml', blob)
+        pkg_item.prettify_xml()
+        assert pkg_item.blob == (
+            '<?xml version=\'1.0\' encoding=\'UTF-8\' standalone=\'yes\'?>\n'
+            '<foo>\n'
+            '  <bar/>\n'
+            '</foo>\n'
+        )